The present invention relates generally to the suppression of electromagnetic interference within an electrical system, and more particularly to the suppression of high frequency electromagnetic noise signals transmitted between a sub-system and a power sub-system within an overall system, such as a computer system.
The present invention applies to any electrical or electronic system such as computer system. To those skilled in the art of computer hardware technology, it is understood that computer systems include a power source sub-system and a computer sub-system. The computer sub-system includes all hardware components other than those included in the power source sub-system. The two sub-systems are typically physically separated within a housing by a partition. A bus bar, known to those in this field, forms a conduit for DC power from the power source sub-system to the computer sub-system. The bus bar usually carries a large amount of current to the computer sub-system in order for the computer sub-system to properly operate.
A specific problem with prior art computer systems is that electromagnetic interference (EMI), which can further be described as a high frequency alternating current noise signal originating in the computer sub-system, is transmitted via the bus bar from the computer sub-system to the power source sub-system. Thus, it has become a priority to electrically isolate the power source sub-system from the computer sub-system, thereby preventing unwanted EMI signals from reaching the power source sub-system. In this application, electrical isolation as used here is defined as radio frequency (RF) isolation only. It is neither practical nor desirable to include direct current (DC) isolation in this definition. One way of electrically isolating the power source sub-system from the computer sub-system is by providing an RF electrical path from the computer sub-system to another location (other than the power source sub-system) having less RF impedance than either the power source sub-system or the computer sub-system. As is well known in the art, electrical current will follow a path of least resistance. A related problem is found in commercial server applications configured with multiple bus bars, with some of the bus bars having high current and low voltage drop requirements. In this type of commercial server configuration, each bus bar provides a conduit for unwanted EMI signals.
Conventional solutions for the above-discussed EMI related problems typically include some type of a feed-through filter. One specific solution that has been developed is the utilization of a lead-type capacitor, which is a capacitor having a plurality of leads for connection to circuitry external to the capacitor. This solution connects the lead-type capacitor between the bus bar and the housing enclosing the computer sub-system and the power source sub-system. Thus, unwanted EMI signals are bypassed through the lead-type capacitor into the housing, rather than transmitted to the power source. However, the disadvantage of using a lead-type capacitor in this configuration is that lead-type capacitors are not adequate RF solutions because of the parasitic inductance that is unavoidably associated with these type of components. Specifically, lead-type capacitors will not work at frequencies greater than 100 megahertz. Therefore, lead-type capacitors will not properly suppress RF EMI signals greater than 100 megahertz.
A second specific solution to the above-discussed problem is the use of a feed-through capacitor. A feed-through capacitor, while physically capable of suppressing EMI signals, is not a viable solution because it is an expensive component and is expensive to incorporate into a computer system. Feed-through capacitors have the appearance in general of a stud or a bolt such that it is necessary to bore holes in the computer housing and provide attachment on both sides of the feed-through capacitor. These interface connections on either side of the feed-through capacitor become problematic because the connections produce a large DC impedance. It becomes a logistical problem to insure that a DC connection is provided through the feed-through capacitor. Additionally, feed-through capacitors are formed from extremely high dielectric ceramics, which are very brittle. The ceramic can fracture and cause a short inside of the capacitor. In extreme examples, the capacitor can heat up and start on fire.
Thus, there is a need for an apparatus and a method for preventing EMI noise signals from escaping a computer sub-system and entering a power source sub-system via a traditional bus bar. It is desirous to have an apparatus and a method which will be reliable, inexpensive in its components, and inexpensive to implement.
The apparatus of the present invention includes a bus bar connected between the power sub-system and the computer sub-system for providing direct current signals between the power sub-system and the computer sub-system. A dielectric material encompasses the bus bar, while an electrically conducting material encompasses the dielectric material and is connected to the electrically conducting housing. Any electromagnetic interference from the computer sub-system will be transmitted to the electrically conducting housing and returned to the portion of the housing surrounding the computer sub-system via a virtual capacitor formed by the dielectric material positioned between the bus bar and the electrically conducting material.
In one embodiment of the present invention, the bus bar is formed from a copper alloy material in a rectangular shape, the dielectric material is formed from a MYLAR(copyright) brand polyester film composition, and the electrically conducting material is a copper foil material. Additionally, due to the materials used and the configuration of the capacitor, the capacitor has a capacitance of greater than 1500 picofarrods and operate at a frequency of greater than 200 megahertz.
In another embodiment of the present invention, multiple bus bars are utilized between the power sub-system and the computer sub-system. Each bus bar is separated from each adjacent bus bar by either a single dielectric layer or a combination of a single electrically conducting layer positioned between two dielectric layers. Therefore, the present invention encompasses suppressing EMI signals from one or more bus bars.
One aspect of the present invention is the formation of an aperture within a partition of the housing. The partition creates two sub-housings, one sub-housing for the power sub-system and one sub-housing for the computer sub-system. The capacitor formed from the dielectric material located between the bus bar and the electrically conducting material is positioned such that it protrudes through the aperture in the partition. A conductive gasket electrically connects the electrically conducting material to the housing by sealing the aperture around the electrically conducting material.
In yet another embodiment of the present invention, a method of filtering the electromagnetic interference signal between a computer sub-system and a power sub-system is disclosed. The method includes encompassing the bus bar with a dielectric material. The dielectric material is then encompassed within an electrically conducting material. The electrically conducting material is in electrical connection with an electrically conducting housing. A virtual capacitor is thereby formed between the bus bar and the housing, providing a path of least resistance for the unwanted noise signals.
The present invention provides an apparatus and a method which provides a solution for the problem of electromagnetic interference signals, which are a high frequency alternating current noise signals, escaping a computer sub-system enclosure and entering a power source sub-system enclosure. The apparatus electrically suppresses or filters unwanted EMI signals between a computer sub-system and a power sub-system, thereby preventing unwanted noise signals to be transmitted between the computer sub-system and the power sub-system. An electrically conducting housing encompasses both the computer sub-system and the power sub-system, and includes a partition between the computer sub-system and the power sub-system.